Toward the end of Bright Lights: Starring Debbie Reynolds and Carrie Fisher, Reynolds rests on a couch, frail but sparkling after receiving a Lifetime Achievement Award from the Screen Actors Guild. “There’s no business like show business,” she says. Fisher, resting her head on her mother’s shoulder, senses an opportunity. “You know what, I have to say something,” she says, perfectly deadpan. “Everything about it is appealing.” Reynolds frowns intently, and joins in. “Nowhere can you get that special feeling.” The pair work through the impromptu skit, perfectly serious, and perfectly in sync.

There are moments like this peppered throughout Bright Lights, a documentary by Alexis Bloom and Fisher Stevens airing Saturday on HBO that captures the forceful personalities and extraordinary charisma of both women, and their fierce but complex love for one another. The film debuted at the Cannes Film Festival last year, and was originally scheduled to air in March, but was moved up after Fisher and Reynolds died at the end of 2016, just a day apart. Given the context, it functions as an adoring tribute to the two performers, but it’s also a snapshot of the kind of relationship documentarians dream about: two eccentric, outgoing personalities, living in almost too-close proximity, recalling their glory days. Part- Grey Gardens, part-Baby Jane without the malice, Bright Lights is endlessly charming and sometimes deeply moving.

It helps that Reynolds and Fisher are such perfect representatives of their respective Hollywood generations, the first a disciplined, controlled product of the studio system, and the second a messier, unfiltered, unflinchingly honest star, whose candor about her mental-health and addiction issues made her achievements more tangible. Bright Lights gets most of its scenes from Fisher, following her to London, to a Star Wars convention, and around her house, with its quirky decor and errant artifacts (a Princess Leia sex doll, a suitcase named Robert). Reynold’s moments are more discreet, more choreographed. But her wit is razor-sharp, and her harmony with Fisher completely in tune. “I share everything with my daughter, especially the check,” she remarks in one scene.

The film’s structure is loose, almost nonexistent, and its main arc seems to be Fisher’s concern for her mother’s health, which comes across now as sharply poignant. Reynolds continues to book performances, which wear her out, so Fisher accompanies her to a cavernous hall in Connecticut and to a shopworn casino in Vegas, where Reynolds zips across the floor on a motor scooter, almost unrecognizable. “You’ve heard of a tsunami, see, she’s tsu-mommy,” Fisher quips early in the movie. The pair live in separate houses within the same Beverly Hills estate, but they’re a constant presence in each other’s lives. “I usually come to her,” Fisher explains, walking across the lawn clutching a cheese soufflé she’s baked for her mother. “I always come to her.” (“That is a beautiful puff,” Reynolds exclaims when she tastes the wares.)

Bloom and Stevens feature a treasure trove of snapshots, home-movie footage, film scenes, and previously documented family moments, thanks largely to Reynold’s passion for amassing Hollywood memorabilia. (One of the documentary’s subplots features her longtime attempts to found a museum along with her son, Todd, a supporting player in Bright Lights who tends to shrink next to the wattage of his mother and sister.) There are scenes of baby Carrie, perfectly groomed for stardom even as an infant, and even 15-year-old Carrie, compelled by her mother to guest in her cabaret act, singing “Bridge Over Troubled Water” with the power and sass of a teenage Janis Joplin. “My mother wanted to be able to groom me for show business,” Fisher says. “The biggest thing I did that broke [her] heart was not do a nightclub act.”

Fisher allows the filmmakers virtually everywhere. In one scene, she works out with a trainer sent over by Lucasfilm, who tries to throw out her Coca-Cola cans and cigarettes, to no avail. In another, she chats with her friend Griffin Dunne while the pair sits on her bed, recalling how he generously helped her out with the loss of her virginity. The cameras are rolling, too, when she has a manic episode sparked by her distress at Debbie’s frailty in the run-up to the SAG Awards. She huddles on the floor in tears, then later launches into impassioned Hamlet quotes and songs while she’s having her nails done. Her concern for her mother is matched by Reynolds, who frequently tears up when talking to the camera about Fisher’s many battles.

But the overarching sense of the film is that the pair have found an easy peace together, and that Reynolds is battling through each day mostly to be able to spend this time with her daughter. While Fisher insists Reynolds continues to perform because it “feeds her in a way that family cannot,” the impression in watching the pair interact is that their closeness means something more. In some moments, the two almost morph into each other by way of shared duets and one-liners. If Bright Lights is, at times, a sharp reminder of what’s been lost, it’s also convincing evidence that wherever Fisher and Reynolds are now, they’re almost certainly together.